Accompanying recent popularization of computers, an inkjet printer is widely used for printing letters or an image on paper, film, cloth or the like not only at offices but also at homes.
The inkjet recording method includes a system of ejecting a liquid droplet by applying a pressure from a piezoelectric element, a system of ejecting a liquid droplet by generating a bubble in the ink under heat, a system of using an ultrasonic wave, and a system of ejecting a liquid droplet by drawing with an electrostatic force. The ink used for such inkjet recording includes an aqueous ink, an oily ink and a solid (fusion-type) ink. Among these inks, an aqueous ink is predominating in view of production, handleability, odor, safety and the like.
The dye used in such an ink for inkjet recording is required to have high solubility in a solvent, enable high-density recording, provide good hue, exhibit excellent fastness to light, heat, air, water and chemicals, ensure good fixing property to an image-receiving material and less bleeding, give an ink having excellent storability, have high purity and no toxicity, and be available at a low cost. However, it is very difficult to find out a dye satisfying these requirements in a high level. In particular, a dye having good magenta hue or cyan hue and excellent in weather resistance has been desired.
Various dyes and pigments for inkjet recording have been already proposed and are actually used. However, a dye satisfying all requirements is not yet found out at present. Conventionally well-known dyes and pigments having a Colour Index (C.I.) number can hardly satisfy both hue and fastness required for the inkjet recording ink. As dyes improving fastness, azo dyes derived from aromatic amines and 5-membered heterocyclic amines as described in JP-A-55-161856 are proposed. Among these dyes, however, since magenta dyes have undesirable hues in yellow and cyan regions and cyan dyes have undesirable hues in yellow and magenta regions, these dyes have a problem of deteriorating color reproducibility. In JP-A-61-36362 and JP-A-2-212566, inkjet recording inks for the purpose of satisfying both hue and light fastness are disclosed. However, the dyes used therein are insufficient in solubility in water, when they are used in water-soluble inks. These dyes also have a problem of fastness to humidity and heat, when they are used in water-soluble inkjet inks. In order to resolve these problems, compounds and inks described in JP-T-11-504958 have been proposed. Also, in order to improve hue and light fastness, inkjet recording inks using pyrazolylanilineazo are described in Japanese Patent Application No. 2000-80733. However, these inkjet recording inks are insufficient in both color reproducibility and fastness of output image.
Moreover, it has been found that preservability of image is extremely poor, when recorded on exclusive inkjet gloss paper for photographic image quality and hung indoors. The present inventors estimate that this phenomenon results from oxidizing gas, for example, ozone in the air. Further, this phenomenon does not occur upon blocking air flow, for example, by means of putting it into a glass frame.
This phenomenon is especially prominent in the exclusive inkjet gloss paper for photographic image quality so that it is a big problem in the present inkjet recording system in which photographic image quality is one of the important features.